The invention relates to a low-voltage limiting circuit breaker, and more particularly to a low-voltage limiting circuit breaker of high rating.
The document GB-A-1,564,412 describes a low-voltage limiting circuit breaker of high rating comprising
a case;
an opening mechanism comprising at least one energy storage means;
one or more poles each comprising:
a stationary contact part fixed with respect to the case;
a stop fixed with respect to the case;
a movable contact part comprising:
a support movable relatively to the case between a closed position and an open position;
at least one movable contact finger movable relatively to the support between a non-repelled position and a repelled position;
at least one bistable mechanism comprising a spring arranged between the support and the finger in such a way that it passes via a maximum potential energy when the finger and support are situated in a dead point position relatively to one another, that it tends to urge the finger to its repelled position when the finger is situated relatively to the support between its repelled position and the dead point position, and that it tends to urge the finger to its non-repelled posit ion when the finger is situated relatively to the support between its non-repelled position and the dead point position;
the stop being arranged in such a way that when the finger is positioned in its repelled position and the support moves from its closed position to its open position, the finger, once in contact with the stop, remains in contact therewith until the support passes beyond an intermediate rocking position relatively to the case, corresponding to the relative dead point position with respect to the finger,
the opening mechanism being kinematically linked to the support in such a way as to urge the support to its open position when the support is in its closed position.
The spring of the bistable device performs several functions. It is first of all designed to provide a contact pressure between the stationary contact part and the contact finger when the circuit breaker is closed which pressure is relatively independent from the state of wear and the manufacturing tolerances of the circuit breaker. This contact pressure is moreover determinant for the repulsion threshold beyond which the electromagnetic forces will drive the finger to its repelled position. When the finger has pivoted beyond the dead point, the spring also serves the purpose of confirming repulsion and/or of preventing the finger from rebounding, since it prevents the finger from returning to a non-repelled position. Before the circuit breaker can be closed again, the energy storage means of the opening mechanism has to be released, which drives the bar and, with said bar, the support of the movable contact part to the open position, and which enables the finger to pivot to the non-repelled position by cooperation with the stop.
In such a device, the energy storage means of the opening mechanism has to overcome the resistance of the spring of the bistable device. However this passage should preferably take place at the beginning of opening travel in order to limit the dimensions of the circuit breaker compartment where the contacts are located. The support for its part has to pivot at sufficiently high speed, when passing the intermediate rocking position, for the return force of the spring of the bistable device not to give rise to too great a movement of the finger and the stationary contact towards one another after the dead point has been passed.
Consequently, the spring of the opening mechanism has to simultaneously speed up the support and compress the spring of the bistable device. In energy terms, it has to simultaneously supply the spring of the bistable device with the energy necessary for the latter to reach its maximum potential energy state, and supply the support with the kinetic energy necessary for high-speed movement thereof to the open position. Let us also recall that the spring of the opening mechanism also has to achieve on its own high-speed opening of the circuit breaker in the event of tripping on a weak current surge.
To reconcile these requirements, a powerful opening energy storage means is generally provided. However this solution is not without drawbacks since the energy released on opening has to be dissipated in the end of opening travel stops so that the power of the spring is determinant for the cost and dimensions of the circuit breaker. Furthermore, different opening mechanisms have to be provided depending on the number of poles of the circuit breaker. Let us recall that not only single-pole, three-pole and four-pole circuit breakers are encountered, but also, for high ratings where each phase is connected to two poles in parallel or serially, six-pole or even eight-pole circuit breakers.
The dimensioning problem is even more complicated when identical movable contact parts of the identical fingers and bistable devices, using supports, are designed to equip circuit breakers whose opening mechanisms are of different kinds. It is in fact desirable to be able to equip a range of circuit breakers indifferently with a first type of mechanism in which the energy storage means of the opening mechanism also releases the energy required for closing of the circuit breaker, and with a second type of mechanism, called O-C-O (for open, closed, open) in which a closing energy storage means is loaded independently from the position of the contacts and performs loading of the opening energy storage means simultaneously when closing takes place. However the two types of mechanism have different opening kinematics. We thus generally consider that, for a given opening energy, i.e. for a given opening spring, the O-C-O mechanism operates at lower speed at the beginning of opening travel and at higher speed at the end of opening travel.
The object of the invention is therefore to overcome the shortcomings of the prior art and in particular to enable movable contact parts with identical bistable mechanisms to be used for limiting circuit breakers whose opening mechanisms have variable characteristics in particular at the beginning of opening travel. Its object is also to enable the opening mechanism of a limiting circuit breaker to be dimensioned regardless of the number of poles. Another object of the invention is to make speeding-up of the support of a movable contact part at the beginning of opening travel relatively independent from the type of opening mechanism implemented. Another object of the invention is to limit the energy to be dissipated at the end of opening travel, without notably increasing either the opening travel or the dimensions of the apparatus. Another object is to reduce the energy required on opening to a minimum.
According to the invention, these objects are achieved by means of a circuit breaker of the above-mentioned type, wherein each pole further comprises an auxiliary mechanism comprising one or more energy storage means urging the support to its open position over all or part of the travel of the support between its closed position and the intermediate rocking position, but no longer urging the support to its open position beyond the intermediate rocking position. The speeding-up at the beginning of opening travel can thus be adjusted by choosing the power of the second energy storage means judiciously.
Preferably the energy storage means of the auxiliary mechanism do not act on the support when the latter is located between its intermediate rocking position and its open position. Beyond the rocking position, the support does not require much energy to reach its open position, so that the energy provided by the second energy storage means is no longer necessary.
Alternatively, an energy storage means can be provided supplying energy to the support over a part of its travel at least between the closed position and the intermediate rocking position and storing energy over at least a part of the travel of the support between the intermediate position and the open position. This energy storage means may for example comprise a spring whose rest position corresponds to the relative rocking position, acting in compression before this position and in traction beyond it. This enables the energy remaining to be dissipated in the end-of-travel stops of the opening mechanism at the end of opening travel to be limited even further.
Preferably, the energy storage means of the auxiliary mechanism of each pole are such that when movement of the movable support of the pole involved takes place, they release an energy greater than or equal to that necessary to move the bistable mechanism(s) of the pole involved to their maximum potential energy. This arrangement is particularly advantageous for a multipole circuit breaker comprising an operating mechanism common to all the poles. It is then in fact easier to dimension the opening spring independently from the number of poles, while limiting the power of said spring.
According to one embodiment, the circuit breaker comprises in addition latching means. This arrangement fosters movement from the intermediate rocking position to the open position. It therefore enables the kinetic energy required for movement from the intermediate rocking position to be limited. This consequently enables the power of the auxiliary mechanism to be limited and furthermore limits the energy to be dissipated in the end of opening travel stops.
According to a preferred embodiment, the energy storage means of the auxiliary mechanism each comprise a spring arranged between the case and the support. Alternatively, it would naturally be possible to make the auxiliary energy storage means act indirectly on the support, for example on an intermediate part of the kinetic transmission system linking the energy storage means of the opening mechanism to the support. However, the preferred embodiment provides the advantage of limiting the stresses on this kinematic transmission system. Advantageously the case comprises polar compartments each containing one of said poles, the spring of each energy storage means of the auxiliary mechanism of each pole being located in the corresponding polar compartment.
According to one embodiment, the spring is a compression spring arranged inside a cylinder closed by a piston head designed to come into contact with the support and to transmit the force of the compression spring thereto. Alternatively, other types of springs can be envisaged, for example torsion or flexion springs.